1. Field of the Invention
This invention relates to porous polymeric beads that contain a biocatalytic material for use in separating small quantities of organic contaminants from solutions. More particularly, the invention concerns such porous polymeric beads that have finely divided particles of activated carbon dispersed within the polymer. The beads of the invention are particularly efficient in adsorbing potentially toxic organic chemicals from aqueous streams. The biocatalytic material, which is located within macropores of the polymer beads, can consume adsorbed organic contaminants and convert them into harmless gases, while continuously renewing the adsorptive capacity of the activated carbon.
2. Description of the Prior Art
The removal of contaminants from aqueous streams has been an important environmental concern for many years. Numerous methods have been employed to significantly decrease the concentrations of various metals and dissolved organic contaminants from such streams. It is well known that dissolved materials can be adsorbed from solution by particles that have suitable surfaces and then the process can be reversed to recover or dispose of the adsorbed material. A frequently used adsorbing material is granular activated carbon (sometimes referred to herein as "GAC"), which has been used as a slurry or fluidized bed. Powdered activated carbon also has been incorporated into biomass sludges to treat water. Advances are desired over these water-treatment techniques are needed, to achieve lower contaminant concentrations, especially in small streams that contain trace quantities of contaminants.
Various particulate materials have been disclosed for selectively adsorbing specific wanted or unwanted ingredients from aqueous and other streams. For Example, Torobin, U.S. Pat. No. 4,743,545, column 1, line 15, through column 3, line 4, which disclosure is hereby incorporated by reference, provides a review of such techniques. Torobin describes various bioreactors and defines "bioreactor" in its broadest sense, as a biocatalyst in a container and "biocatalyst", as one of a variety of chemically active living microorganisms, such as bacteria, yeast, and the like. Numerous known containers or supports for biocatalysts are described. These include: porous solids, porous organic and inorganic fibers, and microcapsules; solid beads, which may or may not be porous, on which microorganisms may be affixed or immobilized; and hollow semipermeable organic microcapsules, gelatinous microbeads and hollow semipermeable fibers that encapsulate biocatalysts. The bioreactors of Torobin have biocatalyst contained in rigid hollow microspheres. The microsphere wall is formed of sintered inorganic particles. The sintered particles form interconnected voids within the walls and thereby provide paths from the outside surface of the microsphere to the hollow central region in which the biocatalyst is contained. The biocatalyst is immobilized by a semipermeable membrane or gel in the pores or in the entrance to the pores of the wall of the hollow microsphere.
Weiss et al, U.S. Pat. No. 4,144,373 discloses fine porous beads of a composite material for use in separating small quantities of dissolved material from a solution. The composite material comprises a mixture of adsorbent particles, such as carbon among others, and optionally magnetic particles embedded in a porous matrix of a hydrophilic cross-linked organic polymer. The magnetic particles facilitate separation of the adsorbent from the liquid being treated. The porosity of the matrix is determined by the degree of cross-linking. Suitable polymeric matrices are hydrophilic polymers such as polyvinyl alcohol, cellulose, polyamides, and polyols, which are cross-linked with appropriate cross-linking agents.
Seidel et al, International Publication No. WO 91/05859, discloses the removal of metal contaminants from aqueous waste streams by contact with insoluble polymeric beads having an internal pore structure containing immobilized extractants. Polymers such as polysulfones and cellulose acetate, and extractants such as yeast, algae, mold, gums, and chemical compounds are disclosed. The beads are formed by dissolving the polymer in organic solvent, blending the desired biomass or chemical extractants into the polymer solution, and then injecting the resultant mixture into water to form spherical beads of about 1/16- to 1/4-inch (1.6-6.4 mm) diameter. The chemical extractants may be sorbed onto powdered activated carbon, as shown in Example 3 of the publication. The carbon serves, not as an extractant but as an aid in retaining the extractant within the finished bead.
U.S. Pat. No. 4,876,287, Babcock et al, discloses polymeric microporous anisotropic beads impregnated with complexing agents for selective removal of copper, zinc, and iron from plating solutions. The beads are prepared by injecting droplets of a solution of the polymer into a water bath where they are precipitated. Among the polymers disclosed for such use by Babcock et al are polysulfones, polyethylenes, polystyrenes, polyamides, and polymethacrylates. The beads are loaded with 20-90 vol % of the complexing agent after the beads are formed.
Each of the above-described known bead materials have some individual shortcomings, (e.g., such as excessive friability, difficulty in sealing the extractant in microcapsules or fibers, limited capacity, etc.). However, all the known bead materials are limited in how long the beads can remain actively effective in removing the desired material from a stream and in being capable of removing very low concentrations of such materials from the stream. Accordingly, it is an aim of this invention to provide a bioreactor in the form of polymeric beads that can remove low concentrations of contaminants from streams for long periods.